This is probably a delicate one: when I forward declare a class using friend the class is unknown to VAX at the declaration.
Example: file test.h forward declares and test.cpp implements class knowme.
test.h:
class test { friend class knowme; };
File test.cpp:
#include "test.h"
class knowme { };
In test.cpp the class is properly colored as it should, but there is no way that it is known in the header file.
I think that VAX in such cases should just assume that the class exists somewhere.